Broad long term objectives of the research proposal include the development of a behavioral and neuroscience research program examining aging and inhibition in a new way, the inhibition of exogenous orienting. Specifically, it will be examined whether healthy older adults can inhibit exogenous orienting when endogenous attention is focused as well as younger adults do. Both the orienting of attention and the inhibitory mechanisms in cognition are central aspects to both normal and abnormal behavior in younger and older adults. In two experiments healthy younger and older adults will perform an exogenous orienting task in which endogenous attention is either focused or dispersed (within-subjects). Endogenous attention state is determined by instruction. Exogenous attention is oriented by an abrupt onset peripheral cue (square) at the location of either the subsequent target letter (valid cue, 50% probability) or nontarget number (invalid cue, 50% probability). Peripheral cue-target interval will vary (200, 500, 700 ms). Target letter category (vowel or consonant) requires a right or left hand button press (counterbalanced). Event-related brain potentials will be collected in Experiment 2. For both experiments, endogenous attention focus will be assessed with catch trials, randomly presented within each block of trials and across conditions, in which no peripheral cue is presented, and a target letter is presented at one of five locations within the designated range of the dispersed attention state. No inhibition of exogenous orienting will occur when endogenous attention is dispersed (Jonides, 1981). However, if older adults have inhibition deficits related to frontal lobe attentional functioning (Kramer. 1994), then they should have difficulty (be slower) inhibiting exogenous orienting when endogenous attention is focused, unlike younger adults (Yantis & Jonides, 1990). Exogenous orienting inhibition, and age differences, will modulate the amplitude of the N1 ERP component.